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Australia
Asked — Edited
Resolved Resolved by Dave Schulpius!

Sabertooth Synchronous Regenerative Properties

I am planning to use a couple of Sabertooth / Kangaroo combos in my B9 project. The robot will be stationary and will be powered by a plugged in 12 volt power supply. I seem to remember something about the synchronous regenerative properties of the Sabertooth requiring a battery for somewhere to channel the feedback voltage to. My question is how is this connected? Do I connect the battery in parallel with the power supply or can I forget the battery and use diodes to stop the back flow. I have searched on line but cant seem to find what I'm looking for. Am I on the wrong track altogether?

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#8  
Alan, thanks for the interest and insight. I've read that the Sabertooth will do it's regen trick when it's breaking. I read this to be when the motor was slowing down to a stop but I may be wrong. Even so, in my B9 it is possible to move the waist, radar and hip motors attached to the Sabertooth when he's powered down. Much like you mention in your example of pushing a wheelchair around. In my circuit the path back to the battery from the Sabertooth is fully open and the switches work to turn it off because of the diodes. So, even if the sabertooth does regen powered down when I push the motors it will dump into the battery. I'm not really a circuit guy so it's kinda like magic to me. Here's a simple drawing of my concept:


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I've not had any problems with damage and the circuit works perfectly as I describe. *cool*
#9  
@RR, I think it's important to realize that we're not using the battery to power anything. The power supply is doing all that. The battery is just there to dump the extra power into that the Sabertooth generates. That's why the PS is first in the circuit and the battery is second. The diode between the ps and the battery keeps the battery from back feeding the PS and the regen power from the Sabertooth from tripping it. ;) Best of both worlds!
#10  
Excellent, thanks Dave. I haven't done any circuit design since high school 30+ years ago, so I wouldn't have been able to figure this out, but your diagram makes perfect sense. Another thread going in my "this will be useful" folder.

Alan
Australia
#11  
I cant thank you enough Dave :D:D

Please excuse my ignorance, I'm an electrician by trade but electronics knowledge is a little limited, on your schematic, the supply voltage is 24 volts and mine will be 12 volts. Does this alter any of the values of the other components? With the signal from the EZB, is that controlled via your script?

Ps. I have been following your progress on this forum and the B9 Builders site for a while now and I am to say the least, in awe of your B9. Blows my mind!

My build is not as far along as yours, I hope to have the Torso in a week or two from a local B9 vendor, Its been a long time coming, over 12 months. I have built the head section from the collar up, the legs are finished, I have a complete aluminium tread section ready for paint and pretty much all the other goodies to go inside it and the Torso. I hope to be able to spend some serious time on him over the Christmas break.

I've been a bit slack with the pictures. I will need to take some more and post them.

Steve
#12  
Steve, the parts I used will work fine with 12v also. In fact I switched my power supply over to 12vdc and it works just fine. One thing that may be of a concern is if your using a V3 or a V4 EZB. The voltage off the signal pin of the digital port on a V3 is 5v and 3.5 on a V4. If you have a V4 reduce R2 to a 10K resistor or this circuit won't work.

Dont worry about not knowing stuff like this. I'm no wiz kid either on electronics. I'm also an electrician but I don't work on the complex level you work on. I'm a distribution power lineman and work on building and maintaining high voltage power lines. So electronics don't really come natural to me. I just study and build what I need. ;)

Looking forward to seeing what your working on !

@Alan, Glad I was able to help and repay you for some of the help you've given me.:)
Australia
#13  
Dave, I am planning to use V4 EZBs. I have ordered two but I am still waiting for them, soon I hope.

I'm sure, when it comes time, I will have to take you up on your offer of help setting up the Sabertooth / Kangaroo

Thanks again mate :)
Australia
#14  
Hi Dave,

I have made some alterations to your schematic as per your Edit, I think I got it right. Could you please look it over and let me know? I have circled the changes in red.
Note - I will be using an EZB4

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Does the diode D3 need to be rated to carry the full load of the motors? I think the 1N4004 Diodes are only rated to 1 amp.

Kind regards

Steve
:)
#15  
Yes Steve, that looks perfect! Thanks for updating the sketch. What program did you use?

The diode D3 does not need to be rated any different then the other diodes as far as I can tell. It's not carrying any of the motors load. It's only blocking the regen voltage of the Sabertooth from back feeding into the control circuit.

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EDIT: Steve, I have to apologize. Thanks for bringing this up. It seems that you've found a weak link in my circuit. My first answer above was premature and given on the fly when I was at work and distracted. After thinking it through I'm sure you're right. Not only D3 is in question but also the other two (D1 and D2) needs to be rated for either the amp draw of both motors being ran from the Sabertooth or for what the total capacity of what the Sabertooth can draw. In this case the 2X12 Sabertooth is capable of pulling up to 12 amps. You'll want to add .25% for safety so you'll want a diode able to handle 15 amps forward current. However if I want to design for my motors amp draw which is 4 amps then I would only need to have diodes that are rated for over 5 amps which includes the safety overhead. I guess its a choice but it would be safer if you design for the capacity of the Sabertooth. The Mosfet at Q2 is plenty large enough. Its rated for 19 amps and the predriver Q1 is behind Q2 so that is OK. Maybe the reason I haven't seen any problems with these 1 amp diodes burning or even heating up is because my motors don't pull more than a couple amps on startup and then drop off when running steady. Also they only run for short bursts of only up to 10 seconds at most. Still, I'm going to have to replace them with something that is rated for more amps. If you need a diode more than 5 amps it may need to be mounted on or with a heatsink. Again, very sorry for the amiture attampt at circuit design.

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I've found time over the past couple weeks to work on my Kangaroo/Sabertooth powered elbow joint in my B9 arm. It's going to be lifting most of the weight and I need it to be smooth, position and speed controlled by a Kangaroo/Sabertooth through the EZB. The speed needs to be human like. I've made some good progress and have learned more about setting up the Kangaroo for lifting heavy robot arms. My biggest problem was after a successful AutoTune when the arm would move to a desired position and hold it would shake and jerk like a drunk with the DTs. Using the DEScribe software I was able to get this adjusted out so it does not happen. I found that the setting in the Control Tab for Position Deadband (not the Deadband in the All Input section) needed to be increased to keep this from happening. Also under the Advanced section the Response Time needed to be increased also. DE said for vertical lifting like a robot arm the High Speed Gain needed to be changed to Zero but I did not see any noticeable change once I did that. However I'm still fine tuning the settings so I can have a more fluid motion and stop. A big holdup is that there is no documentation on how the settings in some of these control settings windows effect the behaviour of the motor. They are auto set by the AutoTune process and they only say they don't need to be changed in most cases. Well, in my case (and maybe yours) they do need to be changed.

Also I found a real good product that works great for me. It's a SoftPot. I mentioned it before. It replaces a regular 10K pot and is flat and round. I'll try to add a link later but if you search the WWW for Softpot you'll find it. SparkFun sells them but they are out of stock right now. I got mine from Mouser. They make linear and round softpots. I have the round version mounted between the motor and homemade hub I built out of 4" alum angle. A separately bought stylist presses down on the Softpot and send the changing voltage reading as the motor shaft turns back to the Kangaroo just like a regular pot. It works great and takes up no room at all. Perfect for tight places. HOWEVER: you need to add 1K resister to the positive leg or it may overheat when pressed improperly in the wrong place. Also I got a better reading using 5vdc and this resister then the 3.5 that the EZB's ADC ports put out. When attached to a Kangaroo X2 this is not a worry as it supplies 5vdc to any feedback device attached to it.

More to follow. Hope this helps.
Dave Schulpius
Australia
#16  
Thanks Dave,

I simply opened the diagram in paint and altered it from there. Pretty low tech ;)

When making alterations to the settings in the Kangaroo, is this where the TTL to USB cable comes in? How is it connected? I will have to have a look at the DEScribe software and figure that out too.

Awesome work on your B9 arms by the way, I cant wait to see how they turn out. If its anything like the rest of your robot, then they will be a masterpiece in engineering. I can only imagine how hard it is to get fluid human like movement.

Steve Neal
#17  
Steve, I have to apologize. Thanks for bringing this up. It seems that you've found a weak link in my circuit. My first answer above was premature and given on the fly when I was at work and distracted. After thinking it through I'm sure you're right.

Not only is D3 in question but also the other two (D1 and D2) needs to be rated for either the amp draw of both motors being run from the Sabertooth or for what the total capacity of what the Sabertooth can draw. In this case the 2X12 Sabertooth is capable of pulling up to 12 amps. You'll want to add .25% for safety so you'll want a diode able to handle 15 amps forward current. However if I want to design for my motors amp draw which is 4 amps then I would only need to have diodes that are rated for 5 amps which includes the safety overhead. I guess its a choice but it would be safer if you design for the capacity of the Sabertooth. The Mosfet at Q2 is plenty large enough. Its rated for 19 amps and the predriver Q1 is behind Q2 so that is OK.

Maybe the reason I haven't seen any problems with these 1 amp diodes burning or even heating up is because my motors don't pull more than a couple amps on startup and then drop off after they get running steady. Also they only run for short bursts of only up to 10 seconds at most. Still, I'm going to have to replace them with something that is rated for more amps. If you need a diode more than 5 amps it may need to be mounted on or with a heatsink.

Again, very sorry for the amiture attampt at circuit design. *blush*
#18  
Here's a 6 amp diode that Great Plains Electronic sells for .35 each:

Great Plains 6 amp diode

Part Number: 6A4
Diode, Rectifier, 400V, 6A
10% Discount for purchase of 10 or more
Manufacturer: Micro Semiconductor


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Australia
#19  
No need to be sorry Dave, Its far from amiture. I'm no expert either, I just wondered cos I was trying to understand the circuit and how it works. and what each parts role is. As I said previously, I'm really green when it comes to electronics :)
Australia
#20  
Just saw your last post Dave, Thanks so much for all your help :D
#21  
Thanks for the soft hand. You may have missed my last post. If you're only interested in sizing for the motors then this diode may work depending on your total amp draw of the motors.
Australia
#22  
So I have finally gotten to the point of connecting up the waist motor on my B9 to the sabertooth/kangaroo. I wired it through the switching circuit that allows the sabertooth to be switched off from the power supply while remaining connected to the dump battery. All was going well until I connected the battery, The moment I did the motor started up running from the battery. The battery should not feed the sabertooth, its just to dump the regen voltage from the motor. The power supply was not connected at this point. For some reason the Mosfet that switches off the supply to the sabertooth was closing as soon as the battery was connected even though there was no supply to the signal pin. I was getting all sorts of weird voltages in places there should have been no voltage. I spent most of the day on it checking and changing diodes which seemed to be fine some times and not others, changing transistors and mosfets and just generally pulling my hair out..... and quite a bit of swearing.

Long story short, the cause of my woes was the light I was using to work with. It was an electronic fluorescent which most of the time, was quite close to everything and inducing a voltage into the wiring and closing the mosfet and transistor. I worked it out when I moved the light near my multimeter leads, which were just sitting on the table at the time, and the voltage reading went up from zero to about 10 volts. Turned the light off and... Eureka! It works.
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As a result of this ..... setback, I haven't had time to get the sabertooth/kangaroo tuned as yet like I had planned. I may need some help with that one when I get back to it in a few days

Steve
#23  
Good find Steve, that must have been terribly frustrating. Always harder to troubleshoot when the results are not consistent. I usually advise people to change one variable at a time and take notes when tracking down difficult problems, but that wouldn't have helped here since two runs of the same test could have had totally different results.

Alan
Australia
#24  
Yes very frustrating to say the least. Its quite a simple circuit with only a few components and not too much to go wrong... so I thought. I was getting a different voltage in some places each time I checked. I had diodes appearing to passing 12 volts in one direction as you would expect and anywhere between 3 to 9 volts in the wrong direction. I'd pull them out and then they seemed to be fine when tested by themselves. I just couldn't see how the mosfet was closing. had to keep walking away from it or I was going to smash it.... or burst into tears ;)
#25  
Steve, you overcame! Sweet! Aside from feeling frustrated and annoyed you couldn't get as much done as you wanted I bet on some level you feel good about yourself. You didn't let a weird and off the wall odd thing like that kick your butt. A lot of people would have walked away and given up or wouldn't have the understanding of what was happening. I admire your analogical mind and your fortitude (do you admire my use of these big words? lol).

Bottom line; Nicely done!

Have you thought any more about going to the Sabertooth 2x32 where the Power outputs can act as voltage clamps? If you recall this would eliminate the need of the extra switching circuit and dump battery.
Australia
#26  
Hi Dave,

It crossed my mind to change up to the 2x32s but I had already bought two 2x12s and figured it was a waste.... never say never though..... I've already blown so much money on doing things twice and three times till I'm happy with them. I still might get the 2x32s after all.

I'm just off to get a dictionary to look up some of those big words you used ;)

Steve
Australia
#27  
Hi Dave,

I think I found a small error on the Sabertooth switching circuit you gave me a while back. I think it shows the 2N3904 transistor (Q4) pin-out reversed.
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Here is a picture of one I Googled
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I'm not sure if I'm right, Its a bit hard to tell in the schematic which way around Q4 is facing, just thought you might like to know :D

Steve